/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: 86187
 * Date: 2022-04-17
 * Time: 23:43
 */

//Scanner scan = new Scanner(System.in);

import java.util.Scanner;

public class RetNum3 {

    /**
     * 递归求1~n 的和
     * @param n
     * @return
     */
    public static int retNum(int n) {
        if(n == 1){
            return 1;
        }
        return n + retNum(n-1);
    }

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        int n = scan.nextInt();

        int ret = retNum(n);

        System.out.println(ret);
    }
}
